Disk-shaped substrates (for example, so-called wafers) from semiconductor material, which are manufactured, among other things, from polycrystalline and monocrystalline silicon, are needed for the semiconductor, MST (microstructure technology) and photovoltaic industries for manufacturing products of these branches of industry.
To obtain these disk-shaped substrates, blocks or cylinders of these semiconductor materials are cut into disk-shaped substrates by means of wire saws. This is carried out by a cutting process, during which this wire (thickness 200 μm) is pulled in a plurality of windings in parallel through the block or cylinder by means of an abrasive, which is in a so-called slurry. Wafer thicknesses of 270 μm to 320 μm are thus obtained currently. The blocks or cylinders cut into wafers are cleaned after this cutting in a cleaning step to remove the slurry. Since the need for high-purity silicon has increased greatly worldwide, because the manufacturers of wafers are currently unable to deliver sufficient quantities of wafers for the photovoltaic industry, it is necessary that the wafer thicknesses be reduced, especially for this field of application, in order to obtain a larger number of wafers from one block or cylinder. Wafer thicknesses of less than 130 μm are desirable. The separation of such disk-shaped substrates is currently embodied by mechanical gripping or pushing mechanisms, which act on the edges of the wafer and thus lead to an increased percentage of broken wafers. Such a process is described in European Patent EP 0 802 028 A2. The individual wafers are cut off there and brought to the receiving device by means of a conveyor belt.
Another method of separating wafers is described in German Patent DE 199 00 671 A1. The individual wafers are separated from each other in this process by blowing in fluid streams. This kind of separation might be suitable for wafers of standard thicknesses.
The small thicknesses of less than 130 ρm make the wafers, which are already highly susceptible to breakage, even more sensitive to mechanical loads, so that wafer separation processes, which apply compressive, tensile or shearing forces on the wafers, must be avoided as much as possible. This also forbids separation by hand, because this handling also leads to great losses of wafers due to breakage and leads, moreover, to a greatly reduced reproducibility.
It is therefore necessary because of the highly complicated and sensitive handling to automate separation processes as much as possible.